1. Field of the Invention
The present invention relates to a radio paging signal coding control scheme for carrying out the coding control in a radio paging system, and more particularly, to a radio paging signal coding control scheme to be used in the radio paging scheme in which logical channels containing a necessary number of coded paging signals are multiplexed into one frame, and time series digital signals in which a plurality of frames are time division multiplexed are used as modulation signals in modulating and transmitting a carrier according to prescribed transmission rate and N-valued modulation scheme.
2. Description of the Background Art
A known high speed radio paging scheme includes a FLEX-TD (FLEX-Time Diversity) scheme (ARIB (Association of Radio Industries and Businesses (JAPAN)) standard specification: RCRSTD-43A), for example. In this scheme, there are four modes for a combination of transmission rate and modulation scheme, including a 1600 bps/2-valued FSK (Frequency Shift Keying) modulation mode, a 3200 bps/2-valued FSK modulation mode, a 3200 bps/4-valued FSK modulation mode, and a 6400 bps/4-valued FSK modulation mode. These modes can be set frame by frame as shown in FIG. 1, where the setting information is contained in the frame information inserted at a synchronization signal portion. The receiver can receive, demodulate and decode the subsequent bit sequences according to a combination of transmission rate and modulation scheme indicated by that frame information.
In each frame, one, two or four logical channels each having a rate of 1600 bps are multiplexed together according to the above described modes. In this standard specification, the logical channel is called a phase, and phases available for transmission of the paging signal information are phase A alone for the 1600 bps/2-valued FSK modulation mode, phases A and C for the 3200 bps/2-valued FSK modulation mode and the 3200 bps/4-valued FSK modulation mode, and phases A, B, C and D for the 6400 bps/4-valued FSK modulation mode, as shown in FIG. 1.
Schemes for multiplexing phases are shown in FIG. 2A and FIG. 2B for the 3200 bps/2-valued FSK modulation mode and the 6400 bps/4-valued FSK modulation mode.
FIG. 2A shows the case of the 3200 bps/2-valued FSK modulation mode, where the multiplexing is carried out in units of two bits information, one bit from each of the phase A and the phase C. As shown in FIG. 2A, the 2-valued modulated symbol is generated by alternately arranging information bits of the phase A and the phase C. The modulated symbol rate is equal to the coding rate which is 3200 bps. A relationship between the phases and the modulated signal states indicates that the frequency shift of +xcex94F corresponds to the code xe2x80x9c1xe2x80x9d and the frequency shift o xe2x88x92xcex94F corresponds to the code xe2x80x9c0xe2x80x9d.
FIG. 2B shows that case of the 6400 bps/4-valued FSK modulation mode, where the multiplexing is carried out in units of four bits information, one bit from each of the phases A, B, C and D. As shown in FIG. 2B, the 4-valued modulated symbol is generated from information bits of the phase A and the phase B, while the 4-valued modulated symbol is generated from information bits of the phase C and the phase D. The modulated symbol rate is equal to a half of the coding rate which is 3200 bps. A relationship between the phases and the modulated signal states indicates that the frequency shift of +xcex94F corresponds to the code xe2x80x9c10xe2x80x9d, the frequency shift of +(⅓)xcex94F corresponds to the code xe2x80x9c11xe2x80x9d, the frequency shift of xe2x88x92(⅓)xcex94F corresponds to the code xe2x80x9c01xe2x80x9d, and the frequency shift of xe2x88x92xcex94F corresponds to the code xe2x80x9c00xe2x80x9d.
When FIG. 2A and FIG. 2B are compared, it can be seen that the modulated symbol rate is the same in both cases but the signal-to-signal distance (a difference in the frequency shift) between neighboring modulated signals is larger in the case of FIG. 2A. Consequently, errors due to influences such as thermal noises are less likely to occur in the case of FIG. 2A with the lower transmission rate and therefore the reception characteristic is better in the case of FIG. 2A.
In the above described scheme, the number of multiplexed channels increases and more paging traffics can be accommodated for the higher transmission rate so that the subscriber capacity becomes larger. On the other hand, as mentioned above, the reception characteristic at the receiver becomes better for the lower transmission rate. As such, the subscriber capacity and the reception characteristic impose mutually reciprocal requirements so that, as a compromise, it is customary to select the minimum necessary transmission rate that can accommodate the maximum value of the paging traffic for each service providing area.
Now, the coding control scheme in the conventional coding control device will be described with references to FIG. 3 and FIG. 4. FIG. 3 shows a conventional radio paging signal coding control device which comprises a paging data storage unit 1 that receives paging data 10, a frame allocation processing unit 2, a frame information memory 4, a phase allocation unit 5, an empty word detection unit 6, a coding processing unit 7, a transmission buffer storage unit 8 and a transmission unit 9 from which the paging data are transmitted to a paging signal transmission base station (not shown).
In this conventional coding control device, when the phase is not particularly specified in the received paging data, the phase allocation within the frame, that is, which phase among the multiplexed phases is to be used in accommodating the paging signals, is determined by randomly allocating and coding all the phases at the phase allocation unit 5 regardless of the paging signal traffic. For example, when the frame is set to the 6400 bps/4-valued FSK modulation mode by the frame information memory 4, the paging signals are coded and accommodated in all four phases starting immediately after the synchronization signal of one frame, as shown in FIG. 4.
For this reason, when the paging traffic is small, the paging signal information is accommodated in a hatched portion of FIG. 4 and the modulated signal state takes one of the four values shown in FIG. 2B. Also, empty words in which no paging signal information is accommodated are arranged at the remaining portion of the frame. Namely, only a part of the transmission time has been actually contributing to the information transmission, and much of the transmission power has been wasteful.
Thus in the conventional coding control scheme, the transmission is carried out by using all the phases that can accommodate the maximum value of the paging traffic regardless of how large the paging traffic is, so that the modulated signal state has to obey the prescribed combination of transmission rate and modulation scheme and it has not been possible to expect a better reception characteristic.
Note that the paging traffic varies in time, so that it is also possible to change the combination of transmission rate and modulation scheme at times where the traffic is large and at the other times, but in the case of changing this combination, there is a need for the coding device to change the information within the synchronization signal so that it is necessary to change the basic frame configuration and there is a need for the coding device to interrupt the coding of the paging signals until the changing of the basic frame configuration is completed.
As described, there has been a problem that the higher transmission rate can increase the subscriber capacity but it also degrades the reception characteristic of the receiver, and in the conventional coding control scheme, it has only been possible to realize the reception characteristic that is dependent on the transmission rate selected in accordance with the maximum traffic, regardless of the variation in time of the paging traffic.
Also, when the paging signal traffic increases instantaneously, if the combination of transmission rate and modulation scheme is to be changed in accordance with the traffic amount, there arises a problem in view of the service in that it becomes impossible to continue the coding processing despite of the fact that the traffic has increased so that it becomes impossible to receive paging signals, and in addition there also arises a problem that the traffic that can be accommodated will be rather reduced because empty portions occur along a time direction in the frame.
It is therefore an object of the present invention to provide a radio paging signal coding control scheme capable of improving the reception characteristic of the receiver by carrying out a coding control to determine logical channels for accommodating paging signals such that the transmission rate equivalently becomes as low as possible according to the paging signal traffic, without interrupting the paging signal coding processing while maintaining the combination of transmission rate and modulation scheme for frames.
According to one aspect of the present invention there is provided a radio paging signal coding control device, comprising: a processing unit for multiplexing logical channels containing coded paging signals into one frame, and modulating and transmitting a carrier using time series digital signals in which a plurality of frames are time division multiplexed as modulation signals, according to prescribed transmission rate and N-valued modulation scheme, where N is an integer; and a control unit for controlling the processing unit by determining logical channels to be used for transmission of paging signals among a plurality of available logical channels, by setting priority orders among said plurality of available logical channels such that a number of states of modulated signals becomes less than N when paging signal traffic is small.
According to another aspect of the present invention there is provided a radio paging signal coding control device, comprising: a processing unit for multiplexing logical channels containing coded paging signals into one frame, and modulating and transmitting a carrier using time series digital signals in which a plurality of frames are time division multiplexed as modulation signals, according to prescribed transmission rate and N-valued modulation scheme, where N is an integer; and a control unit for controlling the processing unit by allocating M logical channels to be used for transmission of paging signals at high priority among a plurality of available logical channels, where M is an integer less than N, such that the paging signals are accommodated in said M logical channels at high priority.
According to another aspect of the present invention there is provided a radio paging signal coding control method, comprising the step of: processing paging signals by multiplexing logical channels containing coded paging signals into one frame, and modulating and transmitting a carrier using time series digital signals in which a plurality of frames are time division multiplexed as modulation signals, according to prescribed transmission rate and N-valued modulation scheme, where N is an integer; and controlling the processing step by determining logical channels to be used for transmission of paging signals among a plurality of available logical channels, by setting priority orders among said plurality of available logical channels such that a number of states of modulated signals becomes less than N when paging signal traffic is small.
According to another aspect of the present invention there is provided a radio paging signal coding control method, comprising the steps of: processing paging signals by multiplexing logical channels containing coded paging signals into one frame, and modulating and transmitting a carrier using time series digital signals in which a plurality of frames are time division multiplexed as modulation signals, according to prescribed transmission rate and N-valued modulation scheme, where N is an integer; and controlling the processing step by allocating M logical channels to be used for transmission of paging signals at high priority among a plurality of available logical channels, where M is an integer less than N, such that the paging signals are accommodated in said M logical channels at high priority.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.